1) Field of the Invention
The subject invention relates to a motor assembly, and more specifically to a motor assembly having improved electromagnetic noise filtering and dissipation for use in a vehicle.
2) Description of Related Art
Electric motors are a tremendous source of electromagnetic emissions, noise, or interference (EMI). It is to be appreciated that EMI may refer to either radiated or conducted emissions, noise, or interference, as understood by those skilled in the art. Most automobiles contain a number of electric motors to control the various engine functions, such as pumping hydraulic fluid for braking and steering systems, and for performing other vehicle functions such as operating windshield wipers, electric windows, electric adjustable mirrors, retractable antennas and a whole host of other functions. In addition, electric motors are used extensively in a number of home appliances such as washing machines, dryers, dishwashers, blenders, hair dryers. Due to the prevalence of electric motors and increased electromagnetic emissions standards there is a need for an assembly having differential and common mode filtering.
EMI can be radiated and conducted through electrical lines from such sources as the motor, the control units, and the like. Other sources of interference are generated from equipment coupled to the electrical lines, such as control circuits, computers, switching power supplies, and a variety of other systems, which may generate significant interference which is desired to be eliminated to meet international emission and/or susceptibility standard requirements. Examples of such standards include automotive component EMC specification GMW-3097/3100.
Several other sources of EMI include cross talk and ground bounce. Cross talk in most connectors or carriers is usually the result of mutual inductance between two adjacent lines rather than from parasitic capacitance and occurs when signal currents follow the path of least inductance, especially at high frequencies, and return or couple onto nearby conductors such as conductive tracks positioned parallel with or underneath the signal current track. Ground bounce is caused by shifts in the internal ground reference voltage due to output switching of a component. Ground bounce causes false signals in logic inputs when a device output switches from one state to another.
Differential and common mode currents are typically generated in cables and on circuit board tracks. Controlling these conducted/radiated emissions is necessary to prevent interference with other circuitry or other parts of the circuit generating or sensitive to the unwanted noise. Based upon the known phenomenon of EMI, a variety of filter and surge suppression circuit configurations have been designed as is evident from the prior art. Most electric motor assemblies include multiple inductors and multiple capacitors within a housing of the motor, as well as exterior to the motor, to suppress EMI. However, as packaging space becomes limited, it is more difficult to package these components within the motor housing.
Therefore, X2Y Attenuators has arrived at a compact circuit, a capacitor, that be can be located outside the motor housing and is capable of filtering and suppressing noise generated by the electric motors. Numerous patents disclose the specific structure of the circuit and various uses of the circuit. U.S. Pat. No. 6,509,807 discloses the circuit mounted to a carrier. The carrier and the circuit, when coupled between an energy source and an active load, simultaneously receive and condition the energy propagating to the load in a differentially balanced manner. The conditioning functions provided by the circuit are facilitated, in part, by the electrical connection between the circuit with an external conductive path provided by the carrier. The carrier is connected to an electrical ground, such as an isolated ground, a chassis ground, or earth ground. The carrier is typically a printed circuit board having conductive regions, or tracks, and non-conductive regions, or tracks. The circuit extends across conductive regions and non-conductive regions to connect to a grounding region. U.S. Pat. No. 5,909,350 discloses the circuit used in combination with a motor.
The carrier reduces mechanical and physical stresses such as shock, vibration and various thermal conditions which the circuit would otherwise be subjected to and provides a complete ground shield for the circuit. Because the carrier has a greater surface area then the circuit and a substantial portion of that surface area is covered by metalized ground surface, the carrier acts as a ground shield which absorbs and dissipates electromagnetic interference and over voltages.
However, it has been discovered that when incorporating the carrier and the circuit into the motor assembly, the location of the circuit on the carrier is critical and it impacts the performance of the circuit. Further, it has been determined that soldering motor terminals to the carrier may weaken the connection between the circuit and the carrier which impacts its ability to suppress EMI. If the circuit is located between the terminals, physical stressing, bending, or applying torque to the carrier and the terminal while inserting the terminal through the carrier may cause a failure in the final product, either immediately or later thereby affecting the products overall reliability. Another drawback to using the above described circuit and carrier is that it becomes very tedious to manually handle and mount the circuit on the carrier while it is being assembled. This translates into lower product yields and added expense due to broken or misconnected components. Further, the mounting of the carrier and the circuit outside the motor housing as described in the related art is difficult, while still ensuring a secure connection between the grounding region and the electrical ground.
The prior art assemblies are characterized by one or more inadequacies. Therefore, it would be advantageous to provide a motor assembly having a reliable connection between the terminal and the carrier without lessening the connection between the carrier and the circuit. It would be further advantageous to provide an assembly having a reliable connection between the grounding region of the carrier and the electrical ground to ensure maximum EMI suppression.